1. Field of Invention
This invention relates to wireless communication networks, methods of operation and program products. More particularly, the invention relates to an improved power saving function for wireless LANs: methods, system and program products.
2. Description of Prior Art
In the current IEEE 802.11 specification, Voice Over Internet Protocol (VoIP) telephones and other multimedia devices operate in two power modes: Active or Continuously Aware Mode (CAM) where the mobile listens for traffic and Sleep or Power Saving Mode (PSM) where the mobile remains in a transmit only standby mode. The mobile unit is either exclusively in one or the other. One operating problem is that the telephones must leave their radios in receive mode during the entire duration of the phone call because non voice packets addressed to the telephone may arrive at any time. Such packets could contain data messages terminating the call or for other data applications running on the phone. The messages cannot be dropped. The phone cannot operate in PSM mode because the latency introduced in such a mode is too long to maintain acceptable voice delay. Thus, considerable power consumption takes place during the receive mode.
When a call is established on a VoIP telephones the unit transmits and receives packets containing compressed digitized voice (or possibly video). These packets are quite small (−100 bytes or so) and are sent and received on a periodic basis. For typical VoIP calls using G.729 compression, a 120 byte packet is sent and/or received every 20 to 40 ms. Even at IM bit, the duration of these packets on the air is less than IMs. At higher data rates the duration is even less. It would be desirable if the power could be turned off from the receive unit during the intervals between voice packets since the receiver knows that the next voice packet will not appear prior to some fixed interval. In such a case, the receiver would be powered off up to 90% of the time and would result in dramatic power savings. In current and future devices, the power consumption of the WLAN radio, even in receive mode, is much greater than other digital circuitry such as DSPs and Codecs and hence the savings would occur even though the digital circuitry would still be active. It would be an advance in the art to further improve the power saving capacity of mobile and terminal units in wireless communication networks.
Prior art related to power saving in wireless communication network includes:
(A) U.S. Pat. No. 5,465,392, issued Nov. 7, 1995 discloses a wireless local area network system including a server and a plurality of mobile wireless stations, the server maintains a table of stations active in the network system and monitors the transmission activity of the stations. If no activity is detected from a station for a predetermined time, a series of watchdog messages is sent requesting a response from that station. The stations are battery powered and operate in an “AWAKE” state to receive or transmit messages or in a SLEEP state of low power consumption. The stations return from the SLEEP state to the AWAKE state in time to receive at least one watchdog message, thereby avoiding the stations being undesirably logged out from the table of active stations.
(B) U.S. Pat. No. 6,002,918, issued Dec. 14, 1999 discloses a communications network comprising a cellular local area wireless network includes a plurality of access points connected to a housed computer and each other, and a plurality of mobile units each mobile unit being arranged for association with an access point. The mobile units are arranged to periodically scan for and identify the most eligible access point for association on the basis of the criteria of best quality signal strength and loading factor. In order to identify when mobile units are being removed from a predetermined area, access points having directional antennae are situated adjacent exit points to detect when mobile units are in vicinity. Each mobile unit may include paging facilities, including the capability of transmitting information in a coded form known both to the unit and to a host, and power-saving facilities
(C) U.S. Pat. No. 6,067,297, issued May 23, 2000 discloses a wireless communication system, in particular a wireless LAN includes at least two mobile units, one of the mobile units including an adapter card configured to support embedded access point capability and including an association table for retaining status information concerning other mobile units in the network and message transmit queues allowing the system to operate in power saving polling mode. According to another aspect the invention relates to a wireless communication system including roaming mobile units wherein, when a mobile unit roams from a first access point to a second access point, the first access point only becomes aware of the roam once the mobile unit has transmitted a packet on to the backbone.
None of the prior art discloses a mobile receiver in an IEEE 802.11 wireless local area network (WLAN) operating in a CAM and a PSM concurrently, and experiencing the low latency that is a benefit of the CAM mode while enjoying the power savings benefit of the PSM